Min SQL Dynamic-fråga körs och skickas till en variabel i lagrad procedur

Ta en titt på det här exemplet -

CREATE TABLE table1(
  column1 VARCHAR(255) DEFAULT NULL,
  column2 VARCHAR(255) DEFAULT NULL,
  column3 VARCHAR(255) DEFAULT NULL
);

INSERT INTO table1 VALUES 
  ('1', 'value1', 'value2'),
  ('2', 'value3', 'value4');

DELIMITER $$
CREATE PROCEDURE procedure1(IN Param1 VARCHAR(255), OUT Param2 VARCHAR(255), OUT Param3 VARCHAR(255))
BEGIN
  SET @c2 = '';
  SET @c3 = '';
  SET @query = 'SELECT column2, column3 INTO @c2, @c3 FROM table1 WHERE column1 = ?';
  PREPARE stmt FROM @query;
  SET @c1 = Param1;
  EXECUTE stmt USING @c1;
  DEALLOCATE PREPARE stmt;
  SET Param2 = @c2;
  SET Param3 = @c3;
END$$
DELIMITER ;

-- Call procedure and use variables
SET @Param1 = 2;
SET @Param2 = '';
SET @Param3 = '';
CALL procedure1(@Param1, @Param2, @Param3);
SELECT @Param2, @Param3;
+---------+---------+
| @Param2 | @Param3 |
+---------+---------+
| value3  | value4  |
+---------+---------+